How to Use Percentages Instead of Odds in Gambling

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Do you get confused when you see things like odds and fractions and percentages listed about a gambling game? Did you score well in school when you had to learn fractions? If you did, do you remember much about them now?

Most people know what they use on a regular basis and tend to forget the things that they don’t use often. Fractions fall into the category for most people because they don’t have to use them in everyday life.

Unless you’re a gambler, the chances are high that you don’t have any idea what odds really are. Odds are usually not used by most people on an everyday basis.

All of this makes it difficult for many gamblers to understand what they’re being told or shown when it comes to odds and fractions. But most people have a pretty good grasp on what percentages mean. And even if you aren’t great with percentages, you will be when you finish this page.

It’s easy to change odds and fractions to percentages if you know how. Anyone with a calculator can change them in seconds, and you probably carry around a calculator all the time, because most mobile phones have one built in.

Below you’re going to learn what odds are, how to convert odds to fractions, how to convert fractions to odds, and how all of this applies to gambling. In the final sections, I show you examples from specific games where you can use percentages.

What Are Odds?

Odds are a way of expressing how likely something is to happen. When you flip a coin, the odds are 50/50. This means that you have an equal chance for the coin to land on heads or tails. Anytime the numbers on both sides of the slash line are equal, and it means the chance of each thing happening is the same.

If you’re looking at two possibilities and one thing happens twice as often as the other, you can write the odds as 1/2, which shows that the odds of the first thing happening are actually 1 out of 3, and the odds of the second thing happening are 2 out of 3.

I know this can be a little confusing, and this is why it’s important to understand how to make odds into fractions and percentages.

Odds are simply fractions that aren’t called fractions. A slash line, like the one between the two 50’s in 50/50 is also used to denote a fraction. So 50/50 is simply a fraction of 50 over 50. When you divide 50 by 50, you get one. Odds, or a fraction, that ends up as one when you divide it means that each possibility has the same chance of happening.

The best thing about fractions is you can easily convert them to percentages. Learn how to do this in the next section.

Converting Fractions to Percentages

Now that you know that odds are simply fractions, all you need to learn is how to convert a fraction to a percentage. This is really easy, and you can use the calculator on your phone or computer to make the calculations quickly.

To change a fraction to a percentage, simply follow two rules:

  1. Divide the top number of the fraction by the bottom number of the fraction.
  2. Move the decimal point two places to the right and put a percentage sign, %, on the end.

Here’s an example:

If you have the fraction 7/28, you divide 7 by 28. This gives you a decimal of .25. Now move the decimal two places to the right. So you change .25 to 25. This makes it a whole number, so in this example, you simply drop the decimal. This means that 7/28 is the same as 25%.

If you have a 7 out of 28 chance of something happening, you have a 25% chance of it happening.

I mentioned that when the decimal is at the right end of the number, it means the number is a whole number so you can drop the decimal. You can write 25% as 25.0% or 25.00%. They all mean the same thing. The reason this is important is because some percentages have both whole numbers and decimals.

Here’s an example:

5/8 when divided gives you the decimal .625. When you move the decimal two places to the right, you have 62.5%. This means the same thing as 62 and ½.

The next thing you need to know about converting fractions to percentages involves rounding off your results. This is important because you don’t need to use long strings of decimals at the end of your percentages in most gambling application.

Zach Galifianakis Card Counting Scene In Hangover With Numbers Floating In Air Around Him

All you need are the first one or two numbers to the right of the decimal when you use them for gambling. Rounding is easy; you just follow a couple simple rules.

  1. Find the number you want to round off to. For gambling purposes, this is the first or second number to the right of the decimal point.
  2. Now look at the number to the immediate right of the number you want to round to. If the number to the immediate right is five or higher, round up. If the number is four or lower don’t round up.
  3. After rounding, drop all of the numbers to the right of the rounded number.

Here’s an example:

If you want to round 42.336% to the second number to the right of the decimal, you look at the number to the immediate right of the number you want to round. In this case, the number to the immediate right is a six. This is five or more, so you round up. This makes the number after rounding 42.34%.

If you want to round 42.336 to the first number to the right of the decimal, you look at the number to the immediate right of the first number. In this case, the number to the immediate right is three, so you don’t round up. This makes the rounded number 42.3%.

Now there’s only one more thing you need to know about percentages. It can be a little bit confusing when you have to deal with percentages less than 1%. Look at a series of percentages and see if you know what they mean.

  • 50%
  • 5%
  • .5%
  • .05%

Don’t worry if you don’t know the exact difference between the four numbers, or if you only know what a couple of them mean for sure. It’s not hard to understand what different percentages mean once you get the hang of it.

The first number on the list, 50%, means that something happens half the time, 5 out of 10, or 50 out of 100 chances. It can also be 500 out of 1,000 times or 24 out of 48 times. Most people have an understanding of what 50% means.

The second number on the list is 5%. This means that something happens 5 out of 100 times or 50 out of 1,000 times, or 1 out of 10 times. 5% of a dollar is a nickel, is another way of looking at it.

The next two numbers on the list are where many people start struggling. This makes sense because most people don’t have to work with numbers smaller than 1% in their daily lives.

.5% is the same thing as half a percent. This is less than 1%, so this happens less than 1 out of 100 times. In this case, .5% happens 5 out of 1,000 times.

The final number on the list, .05%, is even smaller than .5%. This happens only 5 out of 10,000 times.

It might make it easier to understand if you look at how often each number on the list happens, one after the other.

  • 50% 5 out of 10
  • 5% 5 out of 100
  • .5% 5 out of 1,000
  • .05% 5 out of 10,000

As you can see, as the percentage gets smaller, the chances of it happening go down. When it moves down like the example above, the chances on the right go up by adding another zero to the end.

Don’t panic if this is still a bit confusing. You don’t need to use percentages smaller than 1% often, and if you do need to use them in gambling, you can use a calculator.

Gambling Applications

Now that you know about odds and fractions and how to change them into percentages, you need to learn how this helps you when you gamble. I’ve put together some specific examples below using real gambling games and situations.

The main percentage you need to understand when you gamble is the house edge. The house edge is the percentage of every bet that the casino keeps as profit. The house edge is based on all the bets made on a game or machine. This means that it’s a long term percentage.

You play one hand at a time or take one spin at a time, but over the years of your life, you might play a million hands or take a million spins. Walk into a casino on a Saturday evening and look at the hundreds or thousands of people gambling.

Players Gathered Around Roulette Table At Atlanta Casino With Gamblers And Patrons In Background Playing On Slot Machines

Many casinos take over a million in bets on a busy day. Some take millions in action every day. Each game and machine has a house edge, and if you know how much action a game has on a given day and you know the house edge you can determine the theoretical profit for the day for that game.

The actual percentage varies a little bit every day, but in the long run, it averages out to the house edge percentage.

Here’s an example:

The casino has a slot machine that has a house edge of 4%, and players make bets totaling $20,000 on a Saturday on the machine. The expected profit on the machine for the day is $800. You simply multiply the 4% house edge times the total amount of the wagers for the day. You change the percentage to a decimal by moving the decimal two places to the right.

Remember that a whole number percentage, like 4%, has a decimal to the right of the number. So 4% is the same thing as 4.0%. When you move the decimal, 4% becomes .04. .04 X $20,000 = $800.

You can use the house edge percentage to determine your expected loss on any game if you know the house edge.

Here’s an example:

You play Jacks or Better video poker on a 9/6 machine and are able to play close to perfect strategy. Because you make a few mistakes, the house edge is .5%. You play 200 hands per hour, and you bet $5 per hand.

Your expected loss is determined by multiplying the house edge of .05%, or .005, times 200 hands per hour times $5 per hand.

.005 X 200 X $5 = $5

Some hours you’re going to lose more than $5, and some hours you’re going to win more than you lose. But if you play long enough using the same numbers, you’re going to average a $5 an hour loss rate.

I always find it easier to learn and apply new skills by putting them into action. These examples can help you learn how to use percentages in real world gambling situations.


Roulette is an easy place to start because the fractions are easy to see and understand. When you bet on one number, the fractional chance of hitting the number is either 1/37 or 1/38. You use 37 on the bottom for a single zero wheel and 38 for a double zero wheel.

Here’s a list of fractions and the correlating percentages for popular roulette wagers.

Roulette Bet Fraction Percentage Single Zero Percentage Double Zero
One number 1/37 or 1/38 2.7% 2.6%
Two numbers 2/37 or 2/38 5.4% 5.3%
Three numbers 3/37 or 3/38 8.1% 7.9%
Four numbers 4/37 or 4/38 10.8% 10.5%
Six numbers 6/37 or 6/38 16.2% 15.8%
12 numbers 12/37 or 12/38 32.4% 31.6%
18 numbers 18/37 or 18/38 48.6% 47.4%

You can compare these numbers to the payout for winning a bet. The nice thing about roulette is that every bet has the same house edge, so you don’t have to try to figure out which bet is best. The house edge is the same on every wager on a single zero wheel, and the house edge is the same on every bet but one on a double zero wheel. The only bet you should never make playing roulette is the basket wager on a double zero wheel.

The house edge on all single zero roulette wagers is 2.7%, and the house edge on all double zero roulette bets other than the basket is 5.26%. The basket bet on a double zero wheel has a house edge of 7.89%.


When you play slot machines  you don’t have to deal with fractions, and the odds are already converted to percentages. The two most important percentages dealing with slot machines are pay back percentage and the house edge.

The pay back percentage is 100 minus the house edge. This means that the house edge is 100 minus the pay back percentage. In other words, the house edge and pay back percentage, when added together, equals 100%.

Here’s an example:

  • A slot machine with a house edge of 6% has pay back percentage of 94%.
  • A slot machine with a pay back percentage of 97% has a house edge of 3%.

Slot machines don’t usually have pay back percentages listed anywhere, and it’s even hard to find the information online. But it’s worth looking for it because you want to play on machines with the highest pay back percentage because these machines have the lowest house edge.


Blackjack offers many opportunities to use percentages. One of the ways you can use percentages in blackjack is when the dealer offers you insurance when they have an ace as their up card.

When the dealer has an ace face up, they ask each player if they want insurance. If you take the insurance wager and the dealer has a blackjack, you get paid 2 to 1 on your bet. You’ve already made a bet at the start of the hand, so when you take the insurance wager, and the dealer has a blackjack, you basically break even of the hand.

For the dealer to have a blackjack, they have to have a face down card worth 10 points. This means that they have to have a 10, jack, queen, or king. What are the odds that they have one of these cards?

You know that the deck of cards has 13 ranks, from two to ace. Four of the 13 ranks complete a blackjack, and nine of the 13 ranks don’t. Here’s how to convert these numbers to percentages.

Four of the ranks complete a blackjack, so the fraction is 4/13. This gives a percentage of 30.77%.

Nine of the ranks don’t complete a blackjack, so the fraction is 9/13. This is a percentage of 69.23%.

The insurance bet pays 2 to 1. This means that for the payoff to be fair, the percentage chance of the dealer not completing a blackjack to the chance of them completing it needs to be 66.7% to 33.3%.

When you make the insurance wager you actually want the dealer to have a blackjack, so for the bet to be fair, you need the chance of them getting a blackjack to be 33.3%. As you can see, the chance is only 30.77%, so you should never take the insurance bet.


Poker is where I use percentages the most. You play with a deck of 52 cards, so you can figure out the percentage chance of all kinds of things while you play. If you want to know your chance of hitting one of your outs on the turn or river, you can easily figure it out based on your number of outs and the number of unseen cards.

Texas Holdem In Mississippi Casino With River Showing While Players Have Cards Hidden
Here’s an example:

You’re playing Texas holdem and flop four to the nut flush. The turn is a blank, and your opponent shove their stack all in. You need to figure out the chance of hitting your flush on the river to determine if you want to call or fold.

You know that there are nine cards that complete your flush. You’ve seen the two hole cards in your hand and four board cards. This means there are 46 cards you haven’t seen, and nine of them complete your flush. Divide the nine outs by the 46 unseen cards, 9/46, and you know the chance of completing your flush on the river is 19.57%.

To make things easier, you can round this up to 20%. This alone is valuable information to have, but it’s even more valuable when you compare the size of the pot after your opponent’s bet to the amount you have to call.

If your opponent bets $100 into a $600 pot, the pot size is $700, and you have to call $100 to see the river. If you divide your call of $100 by the pot size of $700, 100/700, you get 14.3%.

If your opponent bets $100 into a $300 pot, the pot size is $400, and you have to call $100 to see the river. If you divide $100 by $400, 100/400, you get 25%.

Your chance of hitting your flush is roughly 20%, so you need the percentage of your call against the pot size to be lower than 20% for the call to be profitable. In the first example, the number is 14.3%, and in the second example, it’s 25%.

It’s profitable to call when the number 14.3% and you should fold when the number is 25%. This is called pot odds, and most players are taught to use ratios or fractions. Now you know how to use percentages to determine pot odds.

This is only one of the many ways you can use percentages at the poker table. Start looking for other ways to use them. Figure out the percentage chance of getting an ace as your first card. You know there are four aces and 52 cards in the deck, so you simply divide four by 52, 4/52.

Every time you play, look for opportunities to use percentages. Eventually, you’re going to find that you use percentages automatically to help you improve your results.


I find it easier to use percentages than odds and fractions, even though I know how to use odds and fractions. Many gamblers I’ve talked to over the years struggle with odds, but when I show them how to make them into percentages, things start to become clear.

Now that you know how to use percentages when you gamble, you can make better betting decisions. When you make better betting decisions, it gives you the chance to win more often, and it makes your bankroll last longer.

Michael Stevens

Michael Stevens has been researching and writing topics involving the gambling industry for well over a decade now and is considered an expert on all things casino and sports betting. Michael has been writing for since early 2016. ...

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Michael Stevens

Michael Stevens has been researching and writing topics involving the gambling industry fo ...

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